Absorbent articles such as conventional taped diapers, pull-on diapers, training pants, incontinence briefs, and the like, offer the benefit of receiving and containing urine and/or other bodily exudates. Such absorbent articles can include a chassis that defines a waist opening and a pair of leg openings.
Current diaper chassis are made of numerous individual polymeric components that vary not only in terms of their properties, but also in their shape or form. They can be, for example, fibers, strands, fabrics, or films that can possess properties ranging from plastic to elastomeric. For example, plastic films can be found in outer covers and can be made breathable with the use of embedded fillers. Elastomeric films can be found in back ears and side panels, which helps establish improved fit. The elastomeric films may be perforated to provide airflow that helps maintain skin health. Elastic strands can be typically found in the waist and leg band features and can be combined with nonwovens while under large strain to provide high-performance stretch in a gathered state. Also, plastic fibers may appear in the form of nonwoven fabrics and can be found in virtually all components of the diaper chassis, typically made of either carded or spunbond fibers and thermally bonded together to form the desired fabrics.
In order to produce stretch in materials, as mentioned, elastic strands can be combined with inelastic nonwovens while held under large strains (so called “live stretch”). Live stretch obtained with either elastic strands or elastic films are virtually always constructed in the machine direction (MD) with pre-straining prior to assembling them with the inelastic nonwoven layers, using either strips or adhesive or via thermal point bonding. These have been extensively used in the trade and appreciated for the texture appearance of the gathered nonwovens, but end up using large amounts of nonwoven, and thus may not be the most cost-effective route. An alternative to live stretch constructions are so called “zero-strain” constructions, where mechanical activation is used to apply large strains to a laminate that is comprised of an elastic layer and an inelastic nonwoven layer in order to permanently deform the inelastic layer of the laminate and enable the elastic layer to extend and gather. The extent to which the nonwoven experiences permanent damage instead of permanent deformation greatly depends on the type of nonwoven present in the laminate and its ductility, i.e., its ability to sustain large strain deformation at high strain rates. Since it is most desirable for the nonwoven to retain as much of its mechanical integrity during activation as possible, it is preferred to use nonwovens such as the new types of high-toughness activation-friendly spunbond nonwoven fabrics disclosed in a number of patents (U.S. Pat. No. 7,927,698, U.S. Pat. No. 7,781,527, and U.S. Pat. No. 7,960,478, by Autran, etc.), which also have been found to exhibit increased post-activation strength and enhanced softness and loft.
In sum, current diaper chassis construction may include many components under varying conditions. Adding to the complexity and costs, large amounts of glue or adhesives are generally used in assembling the various components into a fully functional chassis. For example, adhesives may be used in the outer cover to attach the thin plastic film used as a fluid barrier to the nonwoven fabric that provides a cloth-like look and feel. Adhesives may be used in stretch elastic back ears or side panels where the adhesively-bonded nonwoven shields against the tacky or blocky nature of the elastic film onto the body side while again providing a soft fabric feel. Or adhesives may be used in the construction of legband or waistband laminates where live stretch strand elastics are sandwiched in between two layers of inelastic nonwovens that gather upon retraction. One difficulty of working with adhesives is achieving the balance between the right application level of adhesive to achieve adequate bond strength with cost and preventing processing issues such as adhesive burn-through with thin films or adhesive bleed-through with nonwovens. The latter can be particularly difficult as it often requires the use of thicker or more complex nonwoven structures that can impose additional survivability issues during activation. Such fine-tuning of nonwoven/adhesive combinations to work properly adds to the cost and complexity of the overall chassis construction. In addition, assembly of some components with adhesives, such as the legbands, waistbands, or stretch back ears, may occur at a site different from the location where the finished absorbent article is made. Thus there is a continuing need for materials and methods of chassis construction that can be cheaper and simpler.
One development to address these needs includes the use of polyolefins as the materials of choice in the design of diaper chassis in their entirety. These low cost resins can be successfully used for the creation of most if not all chassis components described above, including adhesives. In addition, polyolefin-based assemblies have been found to be very amenable to alternative forms of bonding without need for adhesive, such as ultrasonic bonding.
Another way to limit the need for adhesives can be use of an extrusion lamination process to construct bi- and tri-laminates (for example, see US publications 2009/0264844 and 2010/0040826, by Autran, etc.). This can be done by bringing one or two layers of nonwovens onto a freshly extruded and drawn-down film in close contact to each other at the nip of two compression rolls under controlled temperature and pressure conditions, forming a bond between the two layers by mechanical interlock of extruded film into the fibers of the nonwoven carrier web. It is also possible to apply a small amount of adhesive onto the nonwovens prior to combination with the extruded film, that is a lower amount than that which is typically used in adhesive laminate structures, yet an amount that will still achieve the same level of bond strength, in order to expand the range of bonding conditions. Engraved compression rolls may be used to apply various pressure patterns onto the laminate during its construction and introduce gradients in the depth of nonwoven penetration into the film and therefore the amount of bonding that is generated. The principles that guide the formulation of skin layers in the films are a function of the nature of the nonwoven being unwound, especially with regard to its sheath composition, as the skin layer formulation should be thermally/physically/chemically compatible with the nonwoven in order to provide the most adequate bonding conditions and ensure sufficient bonding without compromising the structural and mechanical integrity of the laminate.
A variety of film structures have been created that provide a wide range of mechanical responses upon activation. This ranges from high-performance elasticity with high recovery to plastoelasticity with a combination of permanent set and partial elastic recovery. The latter have been referred to in the past as “plastoelastic” films, as they possess some amount of permanent set as a result of a first drawing cycle (from the plastic component) and some amount of elastic recovery observed during subsequent cycles (elastic component). The relative amount of each can be tailored to satisfy the need of any particular design that aims to provide conforming garments with superior flexibility in their design, plus lower construction costs. This plastoelasticity is not strictly limited to films, as even nonwovens have been formulated to possess this type of physical deformation behavior.
Therefore, it is an object of the present invention to provide an absorbent article chassis constructed only or predominantly with thin extrusion bilaminates, moving away from the current approach of handling separately backsheet and elastic films, elastic strands, and nonwovens and having to handle large amounts of adhesive, in multiple locations. One object of the present invention is to provide multilayer stretch laminates that provide a finer distribution of the elastic and plastic components in the stretch laminate structures. Another object is to provide dual bilaminates, wherein two thin stretch film-based bilaminates are brought together.